1. Field of the Invention
This invention relates generally to connective mechanical joints; and more particularly to a joint that permits relative rotation of the interconnected articles--through large angles, and about an axis having virtually any arbitrarily selectable orientation. The joint can be adapted to transmit a force or a flux between the articles.
2. Prior Art
Known connective joints may be considered in three very broad categories: the hinge, which provides large-amplitude rotation between two hinged elements, but only about a single axis; the ball-and-socket joint, which provides rotation about arbitrarily selectable axes, but usually with limited range of rotation; and the universal joint, which is in effect a two-stage hinge.
Both large-amplitude rotation and a wide range of rotational axes are achieved with a universal joint by combining two hinges in series, generally at right angles. The selection of rotational axes is essentially arbitrary if rotation is permitted about one or both points of attachment of articles to the universal joint--for example, if the articles interconnected by the joint are rotatable shafts.
With a ball joint, rotational range is particularly limited when a fluid flux is to be transmitted across the joint--as, for example, in a liquid-transmitting joint such as a shower head.
In two different senses, torque can be transmitted through a hinge or universal joint. First, an article attached to one side of the joint can be rotated by rotating an article attached to the other side of the joint--provided that the rotation is about an axis on which the hinge or universal joint is not free.
(The availability of such an axis for useful purposes depends upon the relative orientation of the two sides of the joint. For example, suppose that the two articles are drive shafts, but the joint is initially operated so that these shafts are mutually at right angles. Now rotation of either shaft about its own axis can be transmitted through the joint to the other, but of course the resulting rotation of the receiving shaft is not about its own axis.)
Force or torque can also be transmitted through a hinge or universal joint in a second sense. For such transmission, a gear or a traction surface is provided on an article at one side of the joint, and a suitably mating drive gear or traction wheel is provided on an article at the other side of the joint. With this arrangement, forcible rotation of the gear or wheel results in operation of the joint itself--i.e., change of the relative angle (or angles) at which the two articles are joined.
In the prior art, it has not been readily feasible to interconnect articles for rotation through large angles about a virtually arbitrary axis, using a single-stage joint. Such connection has been particularly awkward with transmission of force or a flux across the joint.